The overall goal of this project is to determine the factors which govern the efficiency of the sarcoplasmic reticulum in the coupling of ATP utilization to the regulation of intracellular Ca2 ion levels in cardiac muscle. These studies proposed here center initially on a determination of the dynamical structure at the submolecular level of the sarcoplasmic reticulum membrane and its functionally relevant model membranes as determined primarily by X-ray and neutron diffraction. The dynamical structure of the natural and model membranes will be studied "at rest" and during the time-course of Ca2 ion uptake and Ca2 ion release. Through such studies and a correlation of systematic structural and dynamical modification of the membranes with their resulting perturbed energy-coupling efficiencies, we hope to gain insight into the molecular mechanism of Ca2 ion transport and the structural and dynamical factors which govern the degree of energy coupling in this regulatory membrane.